A pseudowire (PW) is an emulation of a native service over a Packet Switched Network (PSN). The native service can be asynchronous transfer mode (ATM), Frame Relay, Ethernet, low-rate time-division multiplex (TDM), SONET/SDH, or the like, while the PSN can be multi-protocol label switched (MPLS), Internet Protocol (IP) network (i.e., either IPv4 or IPv6), Layer 2 Tunneling Protocol Version 3 (L2TPv3), or the like. The PW emulates the operation of a “transparent wire” carrying the native service. There are now many PW standards, the most important of which are IETF RFCs 3985 (PWE3 architecture), 4447 (PW setup using LDP), 4448 (Ethernet PW), and 4553 (Structure-Agnostic TDM over Packet (SAToP) TDM PW), as well as ITU-T Y.1411 through Y.1415, Y.1452 and Y.1453 (ATM, TDM, voice services, and Ethernet PWs), and X.84 (Frame Relay PW).
PW technology is used conventionally to carry a customer's layer two traffic over a service provider's (SP) packet switched network (PSN). Advantageously, PW technology has allowed SP's to migrate traditional layer one and layer two services to a converged PSN. However, no single SP has a network that is ubiquitous or spans the entire globe. In order to connect a client that has geographically-diverse sites spread across the world, the SP has to create a PW that transits over other SP's networks, and may even have to terminate on other SP's networks. This reality has created the need for multi-segment PW (MS-PW) where single-segment PWs (SS-PW) are stitched together at each network boundary to form an end-to-end multi-segment PW that transits through two or more SP's PSNs.
The MS-PW requires a switching provider edge (S-PE) to engage in PW setup mechanisms that are specific to the type of PW that is being stitched end-to-end. A provider edge (PE) is a device that provides PW emulation edge-to-edge (PWE3) to a customer edge (CE). A CE is a device where one end of a service originates and/or terminates. The CE is not aware that is using an emulated service rather than a native service. The MS-PW requires coordination and configuration of all stitched PWs at each S-PE that is present in the PW path. Disadvantageously, such configurations are unwieldy. In addition, each S-PE is cognizant of every MS-PW that is passing through it and hence has to maintain control structure and state for each leading to scalability issues.